1. Field of the Invention
The present invention relates to a device for applying wetting agent to a cylinder of a rotary printing machine.
2. Description of the Related Art
A prior art device for applying a wetting agent to a cylinder in a printing machine is disclosed in German reference DE 29 31 579 C2. In that reference, a wetting agent is applied to a cylinder of a wetting mechanism in a rotary printing machine by nozzles. The nozzles are arranged along the cylinder. To control the dispensing of emerging water relative to the machine speed, an orifice plate having a controllable opening is placed over the width of the printing form. However, a problem with this device is that the spray effects of adjacently arranged nozzles overlap, leading to fluctuations in the quality of the printed image. In addition, the drops produced are relatively large which leaves visible water marks on the printed image, despite being split and distributed in the wetting mechanism. The results are impaired quality and spoilage.
In another prior art device disclosed in Japanese reference JP 4-250 039 A, a wetting device for a rotary printing machine includes a pressurized wetting agent located in a duct box that is sprayed onto a body by nozzles. Pressurized air is blown into the duct box creating a mist which is forced through slots in the duct box wall and onto the cylinder of a wetting mechanism. The requirement of pressurized air and its associated control makes this device and its operation expensive. In addition, the use of pressurized air causes a sometimes hazardous wetting agent mist to emerge into the surrounding environment.
In yet another prior art device for wetting a cylinder disclosed in German reference DE PS 571 854, a suction nozzle operated, expensively, with pressurized air produces a jet of liquid that is repeatedly broken up on an impact plate and a reflector. The thus created mist then reaches the plate cylinder in an uncontrolled and unreliable fashion.
Furthermore, it is also common to employ the nozzles of a spray wetting mechanism for wetting agent dosing in pulse operation such, for example, as disclosed in European patent EP 0 325 381 B1. In spite of the good distribution achieved by such discontinuous application in a multi-roller wetting mechanism, the danger exists that the printing form will be unevenly inked and the print quality impaired. In addition, pulse control systems are expensive.